A latened catalytic strategy for low cure thermoset powder coating by post-dry-blending technique

Abstract

Conventional thermoset powder coatings typically require curing at a high temperature of 190 °C for a minimum duration of 15 min, which poses challenges when applying them to heat-sensitive substrates and results in elevated energy costs. A solution known as low-temperature-curing powder coating (LCPC) has been developed to address this issue. By normally incorporating the curing catalyst into the coating system via hot extrusion, LCPC can achieve either a reduced curing temperature or a shortened curing period. However, the current extrusion method used for catalyst incorporation leads to undesirable side effects, such as compromised surface quality, shorter shelf-life and a narrower operational window for the hot-extrusion process involved in producing powder coatings. To overcome these challenges, a new strategy is proposed in this study, in which the tailor-made nano-catalyst is post-dry-blended into the powder coating instead of subjecting it to hot treatment with coating ingredients. This dry-blending catalyst (DBC), encapsulating nanosized fumed silica with catalysts by impregnation method, is introduced to the powder coating system before spraying, eliminating the need for hot-kneading into the powder coating system at the beginning. The DBC is attached to the surface of the particle realizing the interparticle contact mode and latening the catalysis. The dry-blended low-temperature-curing powder coating (DB-LCPC), containing a 0.03 % dosage of onium salt and 0.035 % of 2-methylimidazole, is identified as the optimum formulation due to its excellent surface quality, prominent chemical and mechanical characteristics. The sample successfully achieved low-temperature curing or a shortened curing time while maintaining excellent mechanical properties and chemical resistance. Furthermore, it exhibited superior coating appearances and a longer shelf-life compared to the hot-extruded sample. This novel DBC method has the potential to greatly enhance the adoption of low-temperature-curing powder coatings.